Definition
On a Standard Instrument Departure (SID) or other instrument procedure, the highest altitude at which an aircraft may fly along a specified segment. Maximum altitudes are charted with the altitude figure underlined and may be imposed for airspace, terrain clearance from above (such as overlying airspace), traffic separation, or procedure design reasons. The pilot must not exceed the published maximum altitude on that segment.
Plain English
A ceiling for that part of the route. You can fly at that altitude or below it, but you must not climb above it.
Context Anchor
Seen on SID charts during instrument departures, often as an “at or below” altitude restriction at a named point along the route.
Derivation
“Maximum” comes from a Latin word meaning “greatest.” That fits the aviation use: this is the greatest altitude allowed at that point, not the altitude you are trying to reach.
Why Pilots Care
Keeps the aircraft within published limits that maintain separation from other traffic and comply with ATC routing.
Intuition Check
Do not read “maximum altitude” as the best or expected altitude. Read it as a ceiling: you may not go above it while that restriction applies.
Example Sentence 1
The SID showed a maximum altitude of 5,000 feet on the initial segment, so the crew leveled off there until cleared higher.
Example Sentence 2
We climbed to but did not exceed the published maximum altitude until ATC issued a higher clearance.